Many systems are provided aboard aircrafts, which consist of mobile parts which have to move.
Wing elements (for example an aileron, a flap, an air brake), elements of the landing gear (for example a landing gear strut movable between an extended position and a retracted position, or a plunger of a brake of a wheel which slides relative to brake friction members), elements making it possible to implement variable geometry turbines, elements of a pump or a fuel metering mechanism, elements of the thrust reversers, elements of a propeller pitch driving mechanism (for example on an helicopter or a turboprop engine), etc. belong to such mobile parts.
On modern aircrafts, more and more electromechanical actuators are used to implement such mobile parts. As a matter of fact, the advantages of using electromechanical actuators are numerous: simple electric distribution and driving, flexibility, simplified maintenance operations, etc.
An electromechanical actuator conventionally comprises a mobile actuating member which moves the mobile part, an electric motor intended to drive the mobile actuating member and thus the mobile part, and one or more sensor(s) for the various parameters of the electromechanical actuator.
An airborne electric actuating system wherein such an electromechanical actuator is integrated conventionally implements the following functions: definition of a set-point according to the function to be fulfilled (for instance a speed, position or force set-point), measurement of an electromechanical actuator servo-control parameter (for instance speed, position, force), execution of a servo-control loop enabling the electromechanical actuator to reach the set-point, generation of electric current supplying the electric motor, and transformation, by the electric motor, of the electric energy into a mechanical energy which drives the actuating member and thus the mobile part.
The functions of executing the servo-control loop and generating electric supply current are generally implemented in one or more centralized computer(s): this is called a centralized architecture.
In reference with FIG. 1, a known aircraft brake 1 comprises four electromechanical actuators 2 which are grouped in two distinct arrays of two electromechanical actuators 2. The electromechanical actuators 2 of a distinct array are connected to the same centralized computer 3 positioned in the aircraft bay. The electric motor of each electromechanical actuator 2 receives electric current supplying the centralized computer 3 which the electromechanical actuator 2 is connected to, and each electromechanical actuator 2 transmits measurements of a servo-control parameter to the centralized computer 3 (for instance, measurements of the angular position of the rotor of the electric motor).
Two different configurations of such a centralized architecture thus exist, which can be differentiated by the place where the set-point is defined.
In a first configuration, shown in FIG. 2, means for generating the set-point 5 of each centralized computer 3 define the set-point and transmit it to processing means 6 of the centralized computer 3. The processing means 6 of the centralized computer 3 then execute a servo-control loop. The electromechanical actuator 2 transmits the measurements of the servo-control parameter obtained from a sensor 7 to the centralized computer 3, with said measurements being the servo-control loop feedback signal. The servo-control loop output signal is transmitted to a power module 8 drive, then to a power module 9 of the centralized computer 3 which generates the electric current supplying the electric motor 10 of the electromechanical actuator 2. The electric motor 10 then drives the actuating member 11. Implementing the servo-control loop requires parameters stored in a memory 12 of the centralized computer 3. The power module 9 of the centralized computer 3 is supplied by a supply unit 13 outside the centralized computer 3.
In a second configuration, shown in FIG. 3, the centralized computer 3 is dedicated to the servo-control of the electromechanical actuator 2 and to the generation of the electric supply current, and it no longer defines the set-point which is supplied by another equipment 14 via a digital bus 15, for instance (the transmission is symbolized by reference T1 in FIG. 3).
It should be noted that both such architecture configurations have some drawbacks. The centralized computer 3 thus has to be dimensioned according to the technology of the electromechanical actuator 2 used and the parameters of the servo-control loop have to be adapted to the dimensions of the electromechanical actuator 2 used. The centralized computer 3 and the electromechanical actuator 2 thus tend to be mated, which makes a modification in the electromechanical actuator 2 and a modification in the parameterization of the servo-control loop resulting from the change in technology very complex and very expensive.
Besides, the electric wires between the centralized computer 3 and the electromechanical actuator 2 carry high varying current which requires complex precautions to be implemented to control the electromagnetic emissions.